The present invention provides a protein having an A chain of a ricin-like
toxin, a B chain of a ricin-like toxin and a heterologous linker amino
acid sequence, linking the A and B chains. The linker sequence contains a
cleavage recognition site for a disease specific protease such as a
cancer, fungal, viral or parasitic protease. The invention also relates
to a nucleic acid molecule encoding the protein and to expression vectors
incorporating the nucleic acid molecule. Also provided is a method of
inhibiting or destroying mammalian cancer cells, cells infected with a
virus, a fungus, or parasite; or parasites utilizing the nucleic acid
molecules and proteins of the invention and pharmaceutical compositions
for treating human cancer, viral infection, fungal infection, or
parasitic infection.